1 // SPDX-License-Identifier: LicenseRef-OpenZFS-ThirdParty-PublicDomain
2 /*
3 * Xorshift Pseudo Random Number Generator based on work by David Blackman
4 * and Sebastiano Vigna (vigna@acm.org).
5 *
6 * "Further scramblings of Marsaglia's xorshift generators"
7 * http://vigna.di.unimi.it/ftp/papers/xorshiftplus.pdf
8 * http://prng.di.unimi.it/xoroshiro128plusplus.c
9 *
10 * To the extent possible under law, the author has dedicated all copyright
11 * and related and neighboring rights to this software to the public domain
12 * worldwide. This software is distributed without any warranty.
13 *
14 * See <http://creativecommons.org/publicdomain/zero/1.0/>.
15 *
16 * This is xoroshiro128++ 1.0, one of our all-purpose, rock-solid,
17 * small-state generators. It is extremely (sub-ns) fast and it passes all
18 * tests we are aware of, but its state space is large enough only for
19 * mild parallelism.
20 */
21
22 #include <sys/vdev_draid.h>
23
rotl(const uint64_t x,int k)24 static inline uint64_t rotl(const uint64_t x, int k)
25 {
26 return (x << k) | (x >> (64 - k));
27 }
28
29 uint64_t
vdev_draid_rand(uint64_t * s)30 vdev_draid_rand(uint64_t *s)
31 {
32 const uint64_t s0 = s[0];
33 uint64_t s1 = s[1];
34 const uint64_t result = rotl(s0 + s1, 17) + s0;
35
36 s1 ^= s0;
37 s[0] = rotl(s0, 49) ^ s1 ^ (s1 << 21); // a, b
38 s[1] = rotl(s1, 28); // c
39
40 return (result);
41 }
42